The applicant invented a pinch valve, improved over the conventional pinch valve, which is extremely compact, enhances the durability of a tube body laid inside during valve opening/closing operations, and enables fine adjustment of the flow rate and filed an application for it previously (Japanese Patent Application No. 2001-179027). Explaining this structure with reference to FIG. 8, it is provided with a cylinder body 52 having a cylinder portion 61 having a female screw portion 60 for adjustment of the opening degree at the top inner periphery thereof and an air port 62 communicating with the bottom end of the cylinder portion 61, a cylindrical handle 54 having at a bottom outer periphery thereof a male screw portion 63 adapted to be screwed with the female screw portion 60 of the cylinder body 52 for adjustment of the opening degree, a disk-shaped spring carrier 55 sandwiching the spring 53 with the top end surface of the recess 64 of the handle 54, a connecting bar 56 engaged with the top of the handle 54 and having a bottom end surface connected with the spring carrier 55 so that the spring 53 is sandwiched between the handle 54 and the spring carrier 55, a piston 57 sliding up and down against the inner pheriphery of the cylinder portion 61 in a sealing manner and having a connecting portion 66 suspended from the center of the piston 57 so as to extend in a sealing manner through a through hole 65 formed in the center of the bottom surface of the cylinder body 52, a pressing piece 58 fixed to the bottom end of the connecting portion 66 of the piston 57, and a tube body 59 comprised of an elastic member held inside the body 51 and pressed against the pressing piece 58.
The operation of this pinch valve will be described below. When the handle 54 is turned in the opening direction in a fully closed state wherein the valve is fully closed as shown in FIG. 8, the bottom end surface of the spring carrier 55 is raised via the connecting bar 56. Along with this, the fluid pressure of the fluid flowing through the inside of the tube body 59 and the elastic force of the tube body 59 cause the pressing piece 58 to be pushed up. As a result, the piston 57 rises and the tube body 59 becomes the intermediate opening degree. On the other hand, when compressed air is supplied from the air port 62 to the first space portion 67 in a state wherein the valve is adjusted to the intermediate opening degree, the pressure of the compressed air causes the piston 57 to start to rise while sliding at its periphery against the inner periphery of the cylinder portion 61. Along with this, the top end of the piston 57 rises while compressing the spring 53 via the spring carrier 55 and the pressing piece 58 rises via the connecting portion 66 suspended from the piston 57. Finally, the top end surface of the pressing piece 58 reaches the top end surface of the oval slit formed at the bottom end surface of the cylinder body 52, whereupon the rise of the piston 57 and the pressing piece 58 stops and the pinch valve becomes the fully opened state.
Further, when the supply of air from the air port 62 to the first space portion 67 is stopped and the valve is opened to the atmosphere in the fully opened state, the piston 57 starts to descend due to the resiliency of the spring via the spring carrier 55 abutting against the spring 53 Along with this, the pressing piece 58 also descends via the connecting portion 66 suspended from the piston 57. Finally, the bottom surface of a flange 68 of the connecting bar 56 reaches the bottom surface of the recess 64 formed at the top of the handle 54, whereupon the descent of the piston 57 and the pressing piece 58 is stopped and the pinch valve is adjusted to an intermediate opening degree. By adjusting the opening degree of the handle 54 in this way, it becomes possible to finely adjust the flow rate.
However, in a pinch valve of the above configuration, the adjustment of the stroke of the pressing piece for adjusting the opening degree of the tube body is proportional to the amount of turning of the handle 54 and the proportional constant of the same is determined by the pitch of the male screw portion of the handle. Therefore, to adjust the stroke more precisely, adjustment by an extremely small angle of rotation is necessary. This results in the large operation error and therefore makes fine adjustment difficult. To enable finer adjustment, it is sufficient to make the pitch of the male screw portion of the handle 1 smaller, but making the pitch smaller causes problems in strength and in processing precision and therefore is limited.